Frequency translation devices (“FTDs”), such as mixers and frequency converters, are designed to be simultaneously stimulated by two different electrical and/or optical signals at two of three ports. For example, a mixer having a signal input, a local oscillator (“LO”) input, and an output is designed to be simultaneously stimulated by an input stimulus signal and by an LO stimulus signal, which produces a mixing product, such as an intermediate frequency (“IF”) signal, at the output. The LO stimulus signal is also called a “drive signal” or “LO drive” in some instances. Accurate characterization of such devices is important to predict their performance during use. Characterization at high frequencies (e.g. radio and microwave frequencies, and above) typically involves removing the effects of systemic errors, such as impedance mismatches between the FTD, which is also generally known as a device under test (“DUT”), and the measurement system, be removed.
One approach makes scalar network measurements of power into two ports, and the power out of the third port. However, scalar network measurements cannot accurately measure and remove mismatch errors between the test system and the DUT. Furthermore, scalar measurement systems use filters to separate the stimulus and the output signals in systems that use broad-band detectors to measure power incident upon and emanating from the DUT. These filters selectively allow only signals of a particular frequency range to pass. Such filters complicate or limit the capabilities of the test system when the DUT is characterized at many frequencies, since the filters are changed or adjusted as the measurement frequency changes.
Another technique is to use a conventional vector network analyzer. For three-port devices that do not require multiple stimulus sources, a three-port network analyzer with a three-port s-parameter calibration provides a suitable solution. However, for three-port devices that require simultaneous stimulation (multiple input signals) by two independent signal sources, conventional vector networks analyzers do not provide or account for the effects of the second source. A two-port measurement is typically done, using scalar measurements to characterize the second stimulus port, which is the LO port on a mixer, for example. This approach results in significant uncertainty due to the impedance mismatch between the LO port and the measurement system. Additionally, this approach does not provide means to measure transmission terms between the LO port and the other ports of the device, which may be important to completely and accurately characterize the DUT.